1. Field of the Invention
This invention relates generally to wireless telecommunications, and, more particularly, to methodologies and concomitant circuitry for high-speed wireless access services to fixed and mobile telecommunications users.
2. Description of the Background
The Personal Access Communication System (PACS) system provides high performance, low complexity radio technology for interoperable wireless access using licensed and unlicensed frequency spectra in the 2 GHz emerging technologies frequency band. A representative article which discusses both the history and technological innovations of the PACS system is the article entitled xe2x80x9cPACS: Personal Access Communication Systemxe2x80x94A Tutorialxe2x80x9d, authored by Noerpel et al. and published in the IEEE Personal Communications, June 1996, pages 32-43.
It is well-known in the industry that the Orthogonal Frequency Division Multiplexing (OFDM) technology is an effective means of mitigating Intersymbol Interference (ISI) on multipath fading channels when operated in environments where the Root-Mean-Square (RMS) delay spread is a significant impairment.
However, the art is devoid of teachings and suggestions for combining OFDM and PACS to extend the range of applications and capabilities of PACS, especially in an environment wherein the RMS delay spread is significant.
In accordance with the present invention, a so-called Multicarrier Personal Access Communication System (MPACS) system is a highly modular PACS-based system that combines the advantages of OFDM and PACS, as well as the well-known Time Division Multiple Access (TDMA) technology. MPACS is arranged to support higher-speed (higher than the 32 kbps of PACS) wireless access services to fixed and mobile users. For example, nominal user data rates of 32-to-356 kbps are attainable, and ever the higher speed of 768 kbps is possible for short ranges.
A primary design objective for MPACS, at the physical layer system, is that of retaining as many of the link-level system parameters of PACS as possible, in order to minimize incompatibilities between them. In this respect, the same Time Division Multiple Access (TDMA) frame format and approximately the same Radio Frequency (RF) channel structure is deployed in MPACS. For example, the main licensed version of the PACS system parameters that are of interest in the MPACS system are listed in Table 1 below.
The PACS baseband signal is based on a Square-Root Raised Cosine (SRC) transmit filter and has a single-sided 3 dB bandwidth of 96 kHz, and a roll-off factor of xcex1=0.5, resulting in a total single-sided bandwidth of 144 kHz. Since the transmitted signal is double the single-sided bandwidth, the total bandwidth is 288 kHz 5 (this bandwidth is frequently specified as 300 kHz as in Table 1). In MPACS a higher level Quadrature Amplitude Modulation (QAM), that is, above 4-level QAM (which is essentially the same as Differential Quadrature Phase Shift Key (DQPSK) of Table 1) is used to increase the data range beyond the values of Table 1. This use of higher level QAM has an impact on error rate performance and/or achievable range, and provision for each must be accommodated in the design of MPACS.
The shortcomings and limitations of the prior art are obviated, in accordance with the present invention, by a methodology and concomitant circuitry wherein, generally, the advantageous properties of ODFM and PACS are combined, along with TDMA properties, to extend the range and capabilities of PACS.
Broadly, in accordance with one method aspect of the present invention, a method for detecting a stream of incoming complex symbols conveyed by a radio frequency signal at a given carrier frequency over a wireless channel to produce an outgoing set of bits, the incoming complex symbols including cyclic prefix symbols to suppress channel interference, includes: (1) recovering carrier frequency synchronization information and recovering complex symbol timing information from the radio frequency signal; (2) processing the radio frequency signal using the recovered carrier frequency synchronization and the recovered timing information to produce a stream of recovered complex symbols; (3) removing the cyclic prefix symbols from the recovered complex symbols to produce a reduced set of complex symbols; (4) computing the Discrete Fourier transform of the reduced set of complex symbols to produce a set of detected complex symbols; and (5) demodulating the detected complex symbols to generate the outgoing set of bits.
In accordance with another aspect of the invention, the method for detecting a stream of incoming complex symbols conveyed by a time-division multiple-access frame propagated over a wireless channel to produce an outgoing stream of bits, the time-division multiple-access frame being generated by: (a) converting a sequence of input bits into a corresponding set of input symbols wherein each of the input symbols represents a unique plurality of the input bits; (b) partitioning the time-division multiple-access frame into a plurality of slots each having a prescribed bandwidth and assigning one of the slots to the sequence of input bits; and (c) subdividing the prescribed bandwidth of the assigned slot into a plurality of orthogonal frequency division multiplexed (ODFM) subchannels each conveying a corresponding one of the incoming complex symbols, the method includes; (1) processing the incoming stream of complex symbols to produce a corresponding set of input symbols each representing a unique one of the incoming complex symbols and being conveyed by a corresponding one of the ODFM channels; (2) transforming the OFDM channels to generate a set of transformed complex symbols from the incoming complex symbols; and (c) processing the transformed complex symbols to generate the stream of outgoing bits.
Broadly, in accordance with the system aspects of the present invention, these aspects include circuitry commensurate with the foregoing methodologies.